1. Field of the Invention
The present invention relates in general to bowls having an upper bowl portion formed of one plastic material and a lower base portion formed of a second plastic material. This invention particularly relates to such bowls having a side wall or floor formed with bleed passages for the escape of gas generated as the base portion is molded to the bowl portion so as to define an annular boundary between the two different materials.
2. Description of Prior Developments
When molding a plastic bowl using a two-step molding process, it is difficult and costly to mold the bottom portion of the bowl with a diameter larger than the top portion so as to form a truncated-cone shaped profile. That is, when such a bowl is molded from different plastic or rubber materials on the upper and lower portions, an inwardly directed circumferential ledge is generally formed along the external annular boundary line between the two materials.
When building a mold which forms this annular circumferential boundary ledge, it was found that the walls of the upper portion of the bowl had to be virtually perfectly cylindrical rather than conical in order to extract the bowl from the mold. Otherwise, an expensive and complicated split mold was required.
Rather than using an expensive split mold, a two-part, two-material plastic bowl can be molded in the shape of an inverted truncated cone having an outwardly directed ledge defining the external boundary line between the two plastic materials. While this configuration simplifies the mold design, it creates a problem relating to the removal of gas from the mold during molding of the lower portion of the bowl to the upper pre-formed portion.
Accordingly, a need exists for a method and apparatus for molding a plastic pet bowl in the shape of an inverted truncated cone using a simple mold.
A further need exists for such a method and apparatus which effectively and inexpensively bleeds off excess gas during molding.